This application is based upon the European application S.N. 99400014.9, filed Jan. 5, 1999, which we claim as the priority date of this application.
1. Field of the Invention
This invention relates generally to thermo-optical switches, and more particularly to asymmetric thermo-optical switches that use waveguides arms fabricated from materials having different thermo-optical characteristics.
2. Technical Background
The growth in demand for bandwidth has pushed network operators to increase optical network capacity by transmitting many high bandwidth channels through a single fiber. The signal management of these channels would be greatly simplified by using optically transparent switches.
One approach that has been considered involves planar integrated switches. Planar integrated switches are particularly interesting for several reasons. They have a high potential for integration: a plurality of functional elements can be implemented in one planar device. In addition, they are compact and can be relatively inexpensive to produce. Several techniques may be used to achieve optical commutation in a planar device, but one proposal that has been the subject of intense consideration involves thermo-optical switching. This method is particularly advantageous, because it is one of the easiest approaches to implement. Thermo-optical switches operate by selectively changing the refractive index of a waveguide material.
It has been proposed to use polymer materials to implement thermo-optic switches. Polymer materials are well suited for this application. They are relatively easy to handle and can be easily processed to produce waveguides. The refractive indexes of polymer materials exhibit a wide variation in value with respect to temperature. When a polymer waveguide is heated, the large index variations can alter the phase of the signal propagating in the waveguide, or alter the guiding properties of a waveguide itself. Moreover, the change in the refractive index with respect to temperature (dn/dT) is a reproducible and reversible effect. Such switches of this type are already commercially available.
In other approaches, numerous designs have been used to make planar switches. These include Mach-Zehnder interferometers, directional couplers, Y-splitters, and X-splitters. However, one of the main drawbacks of these devices concerns the positioning and geometry of the heater element.
If the heater is not positioned accurately, or the geometry of the heater is not within proper design tolerances, thermal isolation between the arms of the switch will be inadequate, and unacceptable optical cross talk between output ports will result.
Thus, a need exists for a thermo-optic planar waveguide switch that eliminates both the need for designing heating elements that have strict tolerance requirements, and the expensive and time-consuming process of accurately positioning the heating elements on the planar waveguide switch devices.